String searching and extraction in C Sharp (C#) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What method in C# can you use to find the first position of a substring within a string?

You can use the IndexOf() method. It returns the zero-based index of the first occurrence of the substring, or -1 if not found.

beginner

How do you extract a part of a string in C#?

Use the Substring(startIndex, length) method. It returns a new string starting at startIndex and continuing for length characters.

intermediate

What does LastIndexOf() do in string searching?

It finds the last occurrence of a substring in a string and returns its index. If the substring is not found, it returns -1.

beginner

How can you check if a string contains a certain substring in C#?

Use the Contains() method. It returns true if the substring is found anywhere in the string, otherwise false.

intermediate

What happens if you use Substring() with a startIndex that is out of the string's range?

It throws an ArgumentOutOfRangeException. Always ensure startIndex and length are within the string's bounds.

Which method returns the index of the first occurrence of a substring in C#?

A Contains()

B IndexOf()

C Substring()

D LastIndexOf()

IndexOf() returns the position of the first match, while Contains() returns a boolean.

What does Substring(3, 4) do on the string "HelloWorld"?

A "oWol"

B loWo"

C "loWo"

D "loWo

Starting at index 3 (0-based), it extracts 4 characters: 'l', 'o', 'W', 'o'.

If IndexOf() returns -1, what does it mean?

A Substring was not found

B Substring is empty

C Substring was found at the start

D Substring is at the end

-1 means the substring does not exist in the string.

Which method checks if a string contains another string and returns true or false?

A LastIndexOf()

B Substring()

C IndexOf()

D Contains()

Contains() returns a boolean indicating presence of the substring.

What exception is thrown if Substring() is called with an invalid index?

A ArgumentOutOfRangeException

B InvalidOperationException

C IndexOutOfRangeException

D NullReferenceException

ArgumentOutOfRangeException is thrown when indexes are outside the string's range.

Explain how to find and extract a substring from a string in C#.

Think about first locating the substring, then extracting it.

Describe what happens if you try to extract a substring with invalid indexes in C#.

Consider what the program does when indexes are outside the string length.